Specific Energy Dose (SED)

What is SED? Is it better measure of heating than SAR?  
Specific Absorption Rate (SAR) is the mass normalized rate of energy absorption, measured in watts/kg of tissue. Both local SAR (confined to an organ or region) and whole-body-averaged SAR may be quoted.
Specific Energy Dose (SED) is not a rate, but rather the total energy absorbed by the body during an MRI scan. It is usually measured in Joules/kg body weight. The two measures are related by the equation:
SED = SAR x total sequence acquisition time
The SED can be more meaningful than SAR because it reflects the total energy deposited during the entire scanning period. It is possible, for example, for each sequence in an MRI scanning protocol to lie safely within regulatory SAR limits, yet total energy deposition in the patient over the course of the entire exam to be excessive. Some MR manufacturers now compute and report both SAR and SED, and limit scanning in a full exam if the accumulated SED is too high. 

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References
     Barrera CA, Francavilla ML, Serai SD, et al. Specific absorption rate and specific energy dose: comparison of 1.5-T versus 3.0-T fetal MRI. Radiology 2020; 295:664–674.  [DOI Link]
     Carluccio G, Collins CM. Optimization of the order and spacing of sequences in an MRI exam to reduce the maximum temperature and thermal dose. Magn Reson Med 2019; 81:2161-2166.  [DOI Link]
     Greenberg TD, Hoff MN, Gilk TB, et al. ACR guidance document on MR safe practices: updates and critical information 2019. J Magn Reson Imaging 2020; 51:331-338. [DOI Link]
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